1. Field of the Invention
The invention relates to in-device control techniques including an in-station control technique used in an exchange station, such as an ATM exchange, that controls communications of control data between a peripheral device, such as a terminal interface, that accommodates a subscriber line and a control unit that controls the entire exchange station.
2. Description of the Related Art
In an exchange, in order to control peripheral devices, such as terminal interfaces, that are attached to a channel switch and accommodate subscriber lines, it is required to communicate control data between a control unit, such as a processor, that controls the entire exchange and the terminal interfaces.
FIG. 1 is a block diagram showing a first prior art technique for such control data communications. In this prior art technique, in addition to a highway 106 that is connected between a channel switch (SW) 101 and each terminal interface (TERM) 105 and transmits subscriber data, a dedicated line (physical interface) 107 adapted to transmit control data is installed between each terminal interface 105 and a processor interface (PRIF) 104 that is connected to a central processor (CPR) 102 by a bus 103. Control signals are transferred over that dedicated line by what is called an SD (Signal Drive)/SCN (Scan) technique. In this technique, data time intervals on the dedicated line are assigned the bits of respective control signals, and internal devices communicate control signals in these data time intervals.
However, the first prior art technique has a problem that the installation of dedicated-line cables for control data becomes more complex as the configuration of an exchange system grows larger and hence it is not so easy to install more terminal interfaces 105.
On the other hand, ATM (Asynchronous Transfer Mode)-based broadband exchanges have been developed actively. In such broadband exchanges, there is a need of transmission a large amount of control information, such as subscribers"" traffic information, which may occur irregularly, in addition to conventional control signals. However, when the above-described conventional technique is applied to transmission of such control signal, a problem arises in that it is difficult to map a large amount of control signal that may occur irregularly on the data time intervals on the dedicated lines.
FIG. 2 is a block diagram showing a second prior art technique for control data communications which solves the problems associated with the first prior art technique.
In this technique, a control trunk (TMCNT) 207 of the same rank as each terminal interface (TERM) 205 is connected to a channel switch (SW) 201 by a highway 206 adapted to transmit subscriber data. Control data is transmitted between each terminal interface 205 and the control trunk 207 using control cells multiplexed on the highway 206 together with subscriber""s cells. The control trunk 207 is connected by a dedicated line 208 to a processor interface (PRIF) 204 that is connected to a central processor (CPR) 202 by a bus 203.
The second prior art technique allows the control trunk 207 to communicate control data with a large number of terminal interfaces 205. Therefore, control trunks are allowed to be small in number, and the frequency at which their number is increased is also low. For this reason, the installation of cables will not become so complex even if the exchange system configuration grows larger and moreover the installation of more terminal interfaces will be facilitated.
In the second prior art technique, however, not only subscriber cell communications but also control cell communications will be stopped in the event that the highway 206 that transmits subscriber cells develops a fault. In the event of such a highway fault, it becomes impossible to acquire fault information, which makes it difficult to pinpoint a faulty component and retards recovery from the fault.
The object of the invention is to provide a control data communications system which permits communications cables to be installed readily even if the configuration of an exchange system becomes large, avoids the interruption of control data communications even when a fault occurs in a highway for transmitting subscriber cells, and permits a large number of control signals which may occur irregularly to be transmitted over a dedicated line in an efficient manner.
A first mode of the invention supposes an in-station control technique for control data communications between a peripheral device in an exchange station which receives subscriber information in synchronism with a highway clock and makes subscriber information exchange and a control unit in the exchange station. The first mode comprises a peripheral device cable which is connected to a peripheral device and integrally incorporates a subscriber link that is a physical line for transmitting subscriber information in synchronism with the highway clock and a control link that is a physical line for transmitting control data in synchronism with the highway clock, and a control data converter for controlling interfacing between the control data transferred over the control link synchronously with the highway clock and control data that a control unit transmits/receives asynchronously with the highway clock.
According to the first mode of the invention, if it should be necessary for peripheral devices to be increased in number, it is only required that additional peripheral devices be connected to unused connectors mounted on an exchange cabinet by peripheral device cables.
Moreover, even in the event that the transfer of subscriber information is cut due to the occurrence of a fault in the subscriber link, if the control link develops no fault, control data can be communicated between the peripheral device and the control unit.
Furthermore, since the control data is transferred over the control link synchronously with the highway clock on the subscriber link, there is no need of providing anew a special control line and a clock controller for synchronizing the control link, permitting the system hardware scale to be reduced. In general, in an ATM exchange system and the like the frequency of the highway clock is very high, which permits high-speed control data communications with no need for an additional clock controller for the control link.
A second mode of the invention supposes an in-device control technique for controlling data transfer between first and second devices and comprises a direct memory access transfer control section, provided in each of the first and second devices, for performing direct memory access transfer processing between the first and second devices using a first data transfer time interval allocated to a signal line installed between the first and second devices and a data transfer control section, provided in each of the first and second devices, for performing data transfer processing other than the direct memory access transfer processing using a second data transfer time interval allocated to the signal line.
According to the second mode of the invention, the use of the second data transfer time interval allocated to the signal line permits a small number of specific control signals having real-time requirements for device resetting, fault notification, and the like to be communicated efficiently between the two devices as in the prior art techniques and moreover the use of the first data transfer time interval allocated to the signal line permits a large number of control signals which may occur irregularly, such as subscriber traffic information, to be transferred.